There are two ways to include indices into your document. Look at both and decide.

Manually

Set the opts attribute of your document class to contain the packages makeidx. You do that by: <article opts="makeidx">.

Mark all the words you want to be in the index later with a idx tag or cdx tag. If the word you want to index to a location in your document is not within the text you simply write it at the location you want to index with the nidx tag. It´s like the normal idx only the tagged text will be silently dropped in the normal document.